Due to the risk of blood transmitted diseases and various transfusion reactions, it is common practice to collect blood lost by patients from Wounds during surgery for reinfusion back into the patient instead of infusing donated blood. The collected or salvaged blood typically contains high levels of free hemoglobin (Hgb) and cellular debris such as broken cell membranes. High levels of free Hgb are toxic and can cause kidney disease. Therefore, the removal of free Hgb is desirable. Broken cell membranes and other cellular debris must be removed before reinfusion because they may cause blood clotting and/or kidney necrosis. Other undesirable elements in salvaged blood include activated clotting proteins, anticoagulant, activated platelets and coagulation by-products. The effects are cumulative, such that as more blood is salvaged, washed and reinfused, the more undesirable elements are returned to the patient.
The free Hgb, cellular debris, anticoagulant and other undesirable elements are typically removed from salvaged blood by separating the blood into different fractions according to their densities in a rotating centrifuge bowl and washing out the free Hgb, anticoagulant, cellular debris and other undesirable elements with a continuous flow of saline solution. Although it is difficult to detect the presence or absence of cellular debris, anticoagulant and other undesirable elements, it is easy to detect the presence or absence of free Hgb due to its reddish color. Free Hgb levels are relatively easy to measure experimentally and free Hgb washout is proven to correlate well with washout of other undesirable elements. Therefore, it is common practice to concentrate on free Hgb washout in salvaged blood since the other undesirable elements will also be washed out.